Roles and regulation of Epstein-Barr virus microRNAs

Abstract

MicroRNAs are posttranscriptional gene regulators that play important roles in many cellular processes. These short non-coding RNA molecules regulate gene expression by binding to complementary target mRNAs, thereby inducing RNA destabilization and inhibition of translation. Several DNA viruses hijack the cellular miRNA machinery to produce their own miRNAs, which offers opportunities to regulate both cellular and viral gene expression. The human herpesvirus Epstein-Barr Virus (EBV) encodes more than 40 different miRNAs, which are expressed during all stages of the virus lifecycle and in EBV-associated tumours. EBV is carried as a lifelong latent infection in more than 90% of the adult human population. The virus is the causative agent of infectious mononucleosis and is associated with various malignancies of B cell and epithelial origin. In this thesis we provide a detailed analysis of the EBV miRNA expression profiles in EBV-positive cell lines of different origins. We discovered that the organization of the Epstein-Barr virus (EBV) miRNAs in clusters enhances their functional expression. Furthermore, we developed extensive lentiviral tools to express and inhibit specific miRNAs in cells, to be able to study their biological function. By performing whole-genome transcriptome profiling we identified and validated new EBV miRNA targets. We identified several EBV-encoded miRNAs as novel viral immune evasion factors that interfere with the type I IFN signaling pathway, amongst others. Understanding the specific functions of EBV miRNAs leads to new insights into EBV biology that open new avenues for antiviral therapy development by specifically targeting viral and host genes involved in infection and oncogenic transformation.